Radiating transmission lines are deliberately constructed as imperfect transmission lines so that signals in the inner conductor radiate electromagnetic fields outwardly from the line as the electrical signals are being transmitted down the line. The electromagnetic fields radiated from the line can be picked up by mobile receivers located remotely, but in the vicinity, of the line.
Radiating transmission lines can take on several different forms. One form comprises an open braid coaxial cable. Other forms comprise coaxial cables having cylindrical outer sheaths with longitudinal slits to permit radiation.
Radiating transmission lines are commonly used in environments where electromagnetic waves, such as radio frequency waves, do not propagate well. This type of environment exists, for example, in underground environments, such as mine shafts. For example, a worker in a mine shaft using a remote mobile audio device, such as a walkie-talkie, cannot communicate with other workers who also have remote mobile audio stations, because the radio waves cannot propagate long distances down a mine shaft. However, if all of the workers were near a radiating transmission line such that the radio waves from the first worker's audio device could be received by the transmission line, those signals could be transmitted down the line to a head end unit and then re-transmitted down the wire and radiated near the audio devices of other workers. In this way, communication in the mine shaft can be effected.
As underground mines become more sophisticated and utilize electronic devices and machinery of ever more increasing complexity, there is a need to communicate large amounts of data, as well as audio signals, to remotely located data devices within the underground environment. For example, several underground monitoring devices that monitor the location of personnel and machinery require large amounts of data to be transmitted reliably. Furthermore, control of equipment or large machinery requires the ability to transmit large amounts of digital data to and from the underground environment for both monitoring and controlling the machinery. In addition, many of these electronic devices are designed to operate based on specific protocols, and, it is necessary that the data signals satisfy these protocols.
Furthermore, as remote mining increases, more personnel are operating machinery remotely from the surface or designated areas. In these situations, it is necessary for workers located remotely from the mine to be able to visually monitor the activities within the mine, such as by means of digital video cameras. The digital data signals generated by digital video cameras must then be transmitted to the remotely located personnel.
It is also apparent that because of the nature of a mining environment, the equipment and the personnel must be mobile to progress with the substance, such as ore or coal, being mined. Therefore, at least for this reason, a permanent connection to a communication line is not practical. Rather, ever increasing amounts of data must be transmitted through and radiated from the radiating transmission lines.
In order to transmit larger amounts of data in an underground environment, it is generally necessary to increase the bandwidth of the signals being transmitted and radiated from the radiating transmission lines. However, as the bandwidth increases, there is a corresponding increase in the power required to radiate the signal. This is the case because there is a constant power requirement to radiate each additional Hz of bandwidth. In other words, the ratio of “power” to “Hz or cycles of bandwidth” remains constant such that when the bandwidth is increased, there is a corresponding increase in power required to radiate the signal.
Heretofore, signals along the radiating transmission line have been amplified periodically to boost the signal and also improve the radiating characteristics of the signal. However, these types of amplification units generally involve an operational amplifier or a transistor that linearly amplifies the signal. Unfortunately, while these types of linear amplifiers may be used once or twice to amplify wide band data signals, these amplifiers generally cannot amplify a signal having a wide bandwidth sufficiently to propagate the signal through the radiating transmission line an appreciable distance. This is the case, in part, because these types of linear amplifiers amplify not only the signal but also the noise. Even if filters are utilized to filter the signal before and after amplification, there will be an ever increasing noise to signal ratio because of the gain of the amplifier and the increased power level of the signal.
Accordingly, there is a need in the art for a communication system utilizing a radiating transmission line that can communicate data signals to remotely located and mobile data devices similar to a local area network (LAN) while complying with existing protocols used by the data devices. There is also a need for a radiating transmission line communication system that can transmit data signals having a wider bandwidth. Furthermore, there is a need in the art for an amplifier that can reliably amplify a wide bandwidth signal while decreasing amplification and propagation of noise.